This invention is related to the power generation industry and, more particularly, to the field of generator stator coils.
In the power generation industry, power generators have high voltage generator stator coils. As is known in the art, high voltage generator stator coils have a plurality of metal strands and tend to operate at elevated temperatures. Due to the elevated temperatures during operation, partial discharge often occurs. Partial discharge in these systems causes great damage to insulating components positioned on the high voltage generator stator coils. Partial discharge occurs when voltage builds up in certain locations along a high voltage stator coil. Manufacturers and users of high voltage stator coils often have difficulty finding a material suitable for use with high voltage stator coils that will not deteriorate due to elevated temperatures and environmental elements.
Some stator coils, in an attempt to control partial discharge in armature bars, use a plurality of layers of material as seen in U.S. Pat. No. 6,043,582 by Markovitz titled xe2x80x9cStable Conductive Material For High Voltage Armature Barsxe2x80x9d. The stator coil in Markovitz ""582, uses an antimony-doped tin oxide filler material positioned on top and bottom portions of an armature bar. The stator coil in Markovitz ""582 also includes strand insulation positioned to surround each of a plurality of copper strands on the armature bar. The antimony-doped tin oxide filler material is then applied to the top and bottom portions of the armature bar. Antimony-doped tin oxide is chosen as the filler material because, according to Markovitz, it is not susceptible to oxidative decomposition. One problem that arises when using antimony-doped tin oxide, however, is that it does not easily fill voids formed during the manufacturing process of high voltage stator coils. Another problem that arises in such systems is that, although a filler based on antimony-doped tin oxide may not be susceptible to oxidation, it is quite susceptible to the elevated temperatures often found in high voltage stator coils. One further problem with this stator coil is that there is no way for excess voltage to be removed. Accordingly, excess voltage can still accumulate and eventually cause partial discharge.
In view of the foregoing, the present invention advantageously provides a high voltage generator stator coil and methods for protecting the coil from partial discharge. The present invention also advantageously provides an apparatus and method for protecting generator stator coils which are inexpensive, easy to use, and simple to install as understood by those skilled in the art. The present invention still further advantageously provides an apparatus and method for protecting high voltage generator stator coils and surrounding components which are able to sustain exposure to very high temperatures found in high voltage generator stator coils. The present invention also advantageously provides an apparatus that does not contaminate the high voltage stator coil when applied thereto. The apparatus is also advantageously moisture resistant and capable of withstanding environmental elements.
More particularly, high voltage generator stator coil of the present invention preferably includes a plurality of metal strands positioned in a preselected configuration to abuttingly contact one another. The plurality of strands form a high voltage conductor that preferably has a substantially straight portion. The apparatus further includes a conductive resin-rich fleece filler material positioned to make electrical contact with and overlie the plurality of metal strands and an inner corona protector positioned to overlie the conductive filler material and surround the plurality of metal strands. The stator coil also includes groundwall insulation positioned to overlie and surround the inner corona protector and an outer corona protector positioned to overlie and surround the groundwall insulation. The outer corona protector can be advantageously positioned to make electrical contact with the inner corona protector through the groundwall insulation in at least two different locations along the substantially straight portion of the high voltage generator stator coil.
This configuration of the high voltage generator stator coil advantageously allows a conductive resin-rich fleece filler material to fill voids in the high voltage conductor. These voids are a major source of partial discharge and are often formed during the manufacturing process. Voids in the high voltage conductor provide porosity which can be advantageous in certain types of coil construction such as vacuum pressure impregnation. Due to the porosity of the high voltage conductor, the conductive resin-rich fleece filler material can advantageously fill voids on the top and bottom portions of the high voltage generator stator coil, for example. The conductive resin-rich fleece filler material is also advantageously resistant to high temperatures and is weather resistant.
The present invention also advantageously provides a method for forming a high voltage generator stator coil. The method includes abuttingly contacting a plurality of metal strands to form a high voltage conductor having at least a substantially straight portion. The method also includes positioning a conductive resin-rich fleece filler material to contact upper and lower surfaces of the high voltage stator coil and positioning an inner corona protector to electrically contact and surround the conductive resin-rich fleece filler material. The method further includes positioning groundwall insulation to overlie and surround the inner corona protector and positioning an outer corona protector to overlie and surround the groundwall insulation. The method can also advantageously include contacting the inner and outer corona protectors through the groundwall insulation along the straight portion of the high voltage generator stator coil. This connection thereby relieves voltage buildup in the high voltage generator stator coil and prevents partial discharge.